1. Field of the Invention
This invention relates to ink-jet recording ink and an ink-jet recording method using the same.
2. Description of Related Art
A so-called ink-jet system printer, which jets a liquid or fused solid ink from a nozzle, slit, porous film or the like and conducts recording on a paper, cloth, film or the like, has various advantages such as realization of small size, low cost and silent running. A large number of such printers are commercially available as printers for black or full color. Among such printers, a so-called piezo-ink-jet system printer using a piezoelectric device or a so-called thermal-ink-jet system printer which conducts recording by applying thermal energy act onto ink, thereby forming droplets has many advantages including the provision of high-speed printing and high resolution.
Ink-jet recording ink is requested to have many properties and among these properties, to provide a print image free from any defect is important regardless of printing speed and printing pattern.
To satisfy such a requirement, many attempts have so far been made and also put into practical use. For example, it is proposed in Japanese Patent Application Laid-Open (JP-A) No.63-139963 that ink is prepared so that the stability of foams (that is, the height of the remaining foams) after five minutes from start will become 0 mm as measured by the Ross-Miles Test in accordance with JIS K 3362. In Japanese Patent Application Laid-Open (JP-A) No. 2-97577, it is proposed that defect of a print image are prevented by specifying a nitrous acid concentration in ink as 0.2 ppm to 10 ppm. In Japanese Patent Application Laid-Open (JP-A) No. 5-17712, it is proposed that a dissolved gas in ink is removed by permeation through a gas permeation film. Japanese Patent Application Laid-Open (JP-A) No. 4-239067 suggests ink containing a surfactant having an HLB of from 10 to 20. In Japanese Patent Application Laid-Open (JP-A) No. 7-102201, it is proposed that for a specific ink cartridge, an amount of a surfactant added to ink is defined.
In the above exemplified methods, it is considered that the defect of a print image can be prevented to some extent by various actions. It cannot always be said that these methods can suppress the generation of bubbles or foams in the ink, which will cause the defect of a print image by disturbing the jet of the ink from a nozzle, satisfactorily.
Various causes for the generation of bubbles or foams in the passage for ink are known but those attributable to the ink can be classified roughly into the following three causes:
(1) The solubility of a gas represented by air in an aqueous liquid such as ink generally lowers with increase in temperature. Accordingly, when the temperature in the ink in the passage rises, the gas, or air, dissolved in the ink is discharged and becomes bubbles. PA1 (2) When the wettability of the ink with the passage is inferior, air is trapped in the part of the passage inferior in the wettability and becomes bubbles. PA1 (3) When the surface activity of the ink is high, the ink foams at the time of being mixed with outside air, thereby forming not easily removable foams. PA1 (1) when the bubbles formed were small in size and large in number, some bubbles tended to remain in the passage without being released; PA1 (2) when the bubbles showed an excessive increase in size, they blocked up the passage or broke at the time of removal thereof and therefore could not be removed completely; and PA1 (3) when the bubbles had an appropriate size, they did not break and could be removed easily. PA1 (i) having a molecular weight of about 500 or higher, PA1 (ii) having at least one carboxylic acid per molecule, and PA1 (iii) having a laterally symmetric dye structure.
It is, in fact, difficult to remove all of these causes ideally. Particularly in the thermal ink-jet system, ink is subjected to rapid heating by a heater and is then jetted by the pressure of the bubbles formed by boiling of the ink. Heat is then accumulated mainly in the vicinity of the heater, which tends to heighten the temperature of the ink in the passage. Consequently, it is particularly difficult to control the cause described above in (1).
In this way, it is difficult to prevent the very generation of bubbles or foams. Structural countermeasures are therefore generally taken, for example, by designing the structure of the passage so that the bubbles formed in the passage can be released spontaneously from a nozzle opening during printing or by providing a means for removing the bubbles compulsorily from the nozzle opening by suction or the like operation.
Even by the above-described countermeasures in the structure of the apparatus, however, it is in some cases impossible to suitably release and remove the bubbles or foams. Particularly, depending on the kind of the ink used, such defects are recognized frequently.
There remains another problem to be solved relating to a heater failure. Specifically, deposition (so-called kogation) onto the heater (i.e. a section where bubbles are formed and are allowed to grow by heating) generated by a temperature change causes short-frequency of a working electrode of the heater section, thereby making the heater unoperable.
Many proposals have been made as methods to prevent kogation. For example, it is proposed in Japanese Patent Application Publication (JP-B) No. 3-48950 to Japanese Patent Application Publication (JP-B) No. 3-48954, kogation can be prevented by reducing the amounts of iron, silicon, magnesium, calcium and the like in ink which originate from a dye contained therein. However, the kogation occurs depending on the chemical structure of the dye, even if the amount of these substances are reduced. There is accordingly a demand for the development of the ink which does not easily cause kogation even if various dyes are used as colorants.